//At a lemonade stand, each lemonade costs $5. 
//
// Customers are standing in a queue to buy from you, and order one at a time (i
//n the order specified by bills). 
//
// Each customer will only buy one lemonade and pay with either a $5, $10, or $2
//0 bill. You must provide the correct change to each customer, so that the net tr
//ansaction is that the customer pays $5. 
//
// Note that you don't have any change in hand at first. 
//
// Return true if and only if you can provide every customer with correct change
//. 
//
// 
//
// 
// Example 1: 
//
// 
//Input: [5,5,5,10,20]
//Output: true
//Explanation: 
//From the first 3 customers, we collect three $5 bills in order.
//From the fourth customer, we collect a $10 bill and give back a $5.
//From the fifth customer, we give a $10 bill and a $5 bill.
//Since all customers got correct change, we output true.
// 
//
// 
// Example 2: 
//
// 
//Input: [5,5,10]
//Output: true
// 
//
// 
// Example 3: 
//
// 
//Input: [10,10]
//Output: false
// 
//
// 
// Example 4: 
//
// 
//Input: [5,5,10,10,20]
//Output: false
//Explanation: 
//From the first two customers in order, we collect two $5 bills.
//For the next two customers in order, we collect a $10 bill and give back a $5 
//bill.
//For the last customer, we can't give change of $15 back because we only have t
//wo $10 bills.
//Since not every customer received correct change, the answer is false.
// 
//
// 
//
// Note: 
//
// 
// 0 <= bills.length <= 10000 
// bills[i] will be either 5, 10, or 20. 
// 
// 
// 
// 
// 
// Related Topics 贪心算法 
// 👍 176 👎 0


//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    public boolean lemonadeChange(int[] bills) {
        int change5 = 0;
        int change10 = 0;
        for (int bill : bills) {
            if (bill == 5) {
                change5++;
            }
            if (bill == 10) {
                change10++;
                if (--change5 < 0) {
                    return false;
                }
            }
            if (bill == 20) {
                if (change10 > 0 && change5 > 0) {
                    change10--;
                    change5--;
                    continue;
                }
                if (change5 > 2) {
                    change5 -= 3;
                    continue;
                }
                return false;
            }
        }
        return true;
    }
}
//leetcode submit region end(Prohibit modification and deletion)
